• Journal of the Korean Institute of Telematics and Electronics A
• /
• v.33A no.12
• /
• pp.39-46
• /
• 1996

In AlGaAs/GaAs HBT the temperature dependence of DC parameters was investigated over the temperature range between 95K and 580K. The temperature dependence of DC parameters depends on the relative contribution of each of the current components suc as emitter-injection-current, base-injection-current, bulk recombination current, interface recombination curretn, thermal generation ecurrent and avalanche current due to impact ionization within the collector space charge layer in a specific temperature. In this paper we investigated the temperature effects on DC parameters such as V$_{BE,ON}$ current gain, input and output characteristics, V$_{CE, OFF}$, R$_{E}$, R$_{C}$ and analyzed the origins, and extracted the qualitativ econditions for a stable HBTs against the temperature variation. Finally, in order to keep HBTs stable with respect to the variation of temperature, the valance-band-energy-discontinuity at emitter-base heterojunction should be large enough to enhance the effect of carrier suppression at a relatively high temperature. In addition the recombination centers, especially around collector junction, should be removed and the area of emitter and collector junction should be identical as well.

• Proceedings of the KIEE Conference
• /
• summer
• /
• pp.527-529
• /
• 2004

This paper researched leakage current characteristics of EHW insulators(36,000lbs) to artificially contaminated clay and kaolin through construction of long-periods testing facility. Insulators were contaminated and classified into the ESDD level(B, C and D) under IEC Pub. 60507 standards method. As a result of tests, leakage current of the heavily contaminated D level to clay was approximately 2,260 $[\muA]$, which is contaminated to kaolin was approximately 3,200 $[\muA]$, during initial rainfall. However after raining, leakage current of naturally washed contamination insulators was lower at approximately 300 $[\muA]$. As regular temperature $20^{\circ}C$, leakage current increased greatly in case humidity density was over $72\%$. But, leakage current was not influenced by temperature variation in case of regular $\%$ humidity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.04b
• /
• pp.114-117
• /
• 2002

We have studied the dependence of current-voltage characteristics of Organic Light Emitting Diodes(OLEDs) on temperature-dependent variation. The OLEDs have been based on the molecular compounds. N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1, 1'- biphenyl-4, 4'-diamine (TPD) as a hole transport. tris(8-hydroxyquinolinoline) aluminum (III) ($Alq_3$) as an electron transport and Poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) as a buffer layer. The current-voltage characteristics were measured in the temperature range of 10K and 300K. A conduction mechanism in OLEDs has been interpreted in terms of space-charge-limited current(SCLC) and tunneling region.Ā᐀會Ā᐀衅?⨀頱岒ᄀĀ저會Ā저?⨀⡌ឫഀĀ᐀會Ā᐀㡆?⨀쁌ឫഀĀ᐀會Ā᐀遆?⨀郞ග瀀ꀏ會Ā?⨀〲岒ऀĀ᐀會Ā᐀䁇?⨀젲岒Ā㰀會Ā㰀顇?⨀끩Ā㈀會Ā㈀?⨀䡪ഀĀ᐀會Ā᐀䡈?⨀Ā᐀會Ā᐀ꁈ?⨀硫Ā저會Ā저?⨀샟ගऀĀ저會Ā저偉?⨀栰岒ഀĀ저會Ā저ꡉ?⨀1岒ഀĀ저會Ā저J?⨀惝ග؀Ā؀會Ā؀塊?⨀ග䈀Ā切

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.58 no.12
• /
• pp.2402-2409
• /
• 2009

This paper proposed a simple and helpful analysis model of voltage variation in order to predict the voltage variation at PCC (Point of Common Coupling), when a wind turbine is connected in an isolated grid. The PCC voltage flucuates when the wind turbine outputs active power to an isolated grid. This voltage variation is proportional to the product of the line impedance from the ideal generator to the PCC and the wind turbine output current. And It is different according as where wind turbine is connected. To solve the problem of voltage variation, this paper proposed the reactive power control. To verify the proposed analysis model, this paper utilized PSCAD/EMTDC Simulation and the field measurement data of the voltage variation during the wind power generation.

• Proceedings of the KIEE Conference
• /
• 2004.11c
• /
• pp.748-750
• /
• 2004

The pantograph should supply the electrification equipments of a train with the current from the overhead catenary system over a broad range of speeds. For a high-speed electrical train, the dynamic interaction between the pantograph and the overhead catenary system causes the variation of the contact force. As the operational speed increases, the variation of the contact force increases. The contact force variation can cause contact losses, arcing and sparking. If the spark happens between the pantograph and the overhead catenary system, the EMI(electro magnetic interface) and noises may occur. After all, the quality of current collection is deteriorated. This paper deals with the dynamic characteristics analysis between pantograph and catenary system using block pulse function.

• Journal of the Korean Society for Railway
• /
• v.3 no.3
• /
• pp.131-138
• /
• 2000

The design of current collection system of high speed train requires the fundamental understandings for the dynamic characteristics of catenary system and pantograph. The stiffness of catenary system of high speed train has the varying characteristics for the change of contact point with pantograph, since the supporting pole and hanger make the different boundary conditions for the up-down stiffness of a trolley wire. The variation of stiffness results in Mathiue equation, which characterizes the stability of the system. However, the two-term variation of the stiffness due to span length and hanger distance cannot be solved analytically. In this paper, the stiffness variations are calculated and the physical reasoning of linear model and one term Mathieu equation are reviewed. And the numerical analysis for the two-term variation of the stiffness is done for the several design parameters of pantograph.

• Proceedings of the KIEE Conference
• /
• 1997.07b
• /
• pp.452-455
• /
• 1997

It is well known that Variable Structure Controller(VSC) is robust to parameters variation and disturbance but its performance depends on the design parameters such as switching gain and slope of sliding surface. This paper proposes a more robust VSC that is composed of local VSC's. Each local VSC considers the local system dynamics which has narrow parameter variation and disturbance. We optimize the local VSC's by use of Evolution Strategy, and then we use Artificial Neural Network to generalize the local VSC's and construct the overall VSC in order to cover the whole range of parameter variation and disturbance. Simulation on BLDC motor current control has verified the proposed VSC is superior to the conventional VSC.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1998.06a
• /
• pp.343-346
• /
• 1998

Degradation characteristics of the Pr-based ZnO varistor with $Y_2O_3$content (0.0-4.0 mol!%j were investigated. It was appeared that the variation of the J-E characteristics in the reverse direction before and after the applied stress with increasing $Y_2O_3$ content was larger than that of the forward direction but the variation was extrernly small. For all varistor, the leakage current with the stress time during the applied stress somewhat increased initialy but afterthat was almost constant or slightly decreased. The overall varistor voltage and nonlinear coefficient were less than 5%. Especially, in the case of Pr-based ZnO varistor containing 2.0 mol% to 4.0 mol% $Y_2O_3$, the variation of breakdown voltage and nonlinear coefficient was less than 1% and 5%. respectively. As a result, they showed good stability.

• Proceedings of the KIEE Conference
• /
• 2000.07b
• /
• pp.1056-1058
• /
• 2000

Deadbeat technique has been proposed as a digital controller for an UPS inverter to achieve the fast response to a load variation and to conserve a very low THD under a nonlinear load condition. This scheme contains a fatal drawback, sensitivity against parameter variation and calculation time delay. This paper proposes a second order deadbeat current controller, which fundamentally solves the calculation time delay problem and certainly guarantees the robustness of the parameter's variation. This is shown theoretically and practically through simulation and experiment.

• Proceedings of the KSR Conference
• /
• 2000.05a
• /
• pp.598-605
• /
• 2000

The design of a current collection system of high speed train requires the fundamental understandings fer the dynamic characteristics of a catenary system and pantograph. The stiffness of the catenary system of high speed train has the varying characteristics for the change of the contact point with a pantograph, since the supporting pole and hanger make the different boundary conditions for the updown stiffness of a trolley wire. The variation of stiffness results in Mathiue equation, which characterizes the stability of the system. However, the two terms variation of the stiffness due to span length and hanger distance cannot be solved analytically. In this paper, the stiffness variations are calculated, and the physical reasoning of linear model and one term Mathieu equation are reviewed. And the numerical analysis for the two term variation of the stiffness is done for the several design parameters of the pantograph.